1. Field of the Invention
The present invention relates generally to temperature control systems and, more particularly, to apparatus for controlling the temperature of a chemical reaction cell and of reaction components introduced into the cell. The apparatus of the invention is particularly useful in the analysis of biological samples, such as blood or urine, which are reacted with repeatable volumes of reagent at a predetermined temperature.
2. Description of the Prior Art
U.S. Pat. No. 3,857,771 (Sternberg), assigned to the assignee of the present invention, discloses chemical analysis apparatus for determining the glucose content of blood, urine, or other samples. In the apparatus, the sample is introduced into a reaction cell and reacted with a reagent such as glucose oxidase. A resulting rate of change of oxygen concentration is then measured to provide a measure of the glucose content in the sample.
U.S. Pat. No. 3,701,716 (Deuringer et al.), similarly assigned, discloses a semi-automated system for performing such analysis. In the Deuringer et al. system, a reproducible reagent volume is rapidly delivered from a reservoir to a reaction cell and a sample added to the reagent for reaction therewith. After analysis, the cell is completely drained in preparation for delivery of the next reagent volume thereto.
In practice, in the aforementioned systems a reagent volume on the order of 1 milliliter is first delivered to the reaction cell and a substantially smaller quantity of sample, on the order of ten microliters, is then injected into the cell by means of a pipette or other sampling device. Further, the analysis is carried out in a temperature controlled environment since the measurements are temperature sensitive. Typically, where body fluid samples are to be analyzed, the reaction is conducted near body temperature of 37.degree. C. A temperature control system for such apparatus should preferably stabilize the temperature of the reaction cell and of the reagent therein prior to introduction of sample into the cell.
Several temperature control approaches have been employed with analysis apparatus of the foregoing type. In one approach the apparatus itself is enclosed within a temperature controlled housing so that the reaction chamber, the reagent reservoir, the delivery lines between the reservoir and the chamber, and other components are situated in an air bath. Thermal heaters and temperature sensors control the air bath temperature. This approach exhibits a number of disadvantages. First, a relatively large enclosure must be heated. As a result, the system exhibits a slow thermal response time and possible temperature variations at different locations within the enclosure. Moreover, the housing must be well insulated. In addition, opening the enclosure to gain access to the reaction chamber or other system components destroys the temperature equilibrium. Also, certain reagents rapidly deteriorate when maintained at elevated temperatures for prolonged periods, and such can occur when the reagent reservoir is situated within the enclosed air bath.
In a second approach, two separate heaters are employed, one to heat the reaction chamber to the proper temperature and the other to preheat the reagent in the delivery line at a location remote from the reaction chamber. While this approach can eliminate the need for an air bath housing, it requires two separate heaters each with an associated temperature sensor controlling operation thereof. As a result, relatively complex thermal control circuitry is required to control both heaters. Moreover, since the reagent preheater is remote from the reaction cell, the reagent temperature may drop in the time interval after the reagent is discharged from the preheater and before it is supplied to the reaction chamber. In such case, if proper reaction temperature is to be achieved, the reagent must be brought back up to the proper temperature after delivery to the reaction cell, thereby delaying the introduction of sample into the cell and reducing the sample throughput rate of the analyzer.